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.TH IOCTL 2 "June 18, 2020"
.SH NAME
ioctl \- control device
.SH SYNOPSIS
.nf
#include <unistd.h>
#include <stropts.h>

\fBint\fR \fBioctl\fR(\fBint\fR \fIfildes\fR, \fBint\fR \fIrequest\fR, \fB/*\fR \fIarg\fR */ ...);
.fi

.SH DESCRIPTION
The \fBioctl()\fR function performs a variety of control functions on devices
and streams. For non-streams files, the functions performed by this call are
device-specific control functions.  The \fIrequest\fR argument and an optional
third argument with varying type are passed to the device file designated by
\fIfildes\fR and are interpreted by the device driver.
.sp
.LP
For streams files, specific functions are performed by the \fBioctl()\fR
function as described in \fBstreamio\fR(4I).
.sp
.LP
The \fIfildes\fR argument is an open file descriptor that refers to a device.
The \fIrequest\fR argument selects the control function to be performed and
depends on the device being addressed.  The \fIarg\fR argument represents a
third argument that has additional information that is needed by this specific
device to perform the requested function. The data type of \fIarg\fR depends
upon the particular control request, but it is either an \fBint\fR or a pointer
to a device-specific data structure.
.sp
.LP
In addition to device-specific and streams functions, generic functions are
provided by more than one device driver (for example, the general terminal
interface or disk interfaces.)  See \fBtermio\fR(4I)), \fBdkio\fR(4I), etc..
.SH RETURN VALUES
Upon successful completion, the value returned depends upon the device control
function, but must be a non-negative integer.  Otherwise, \fB\(mi1\fR is
returned and \fBerrno\fR is set to indicate the error.
.SH ERRORS
The \fBioctl()\fR function will fail for any type of file if:
.sp
.ne 2
.na
\fB\fBEBADF\fR\fR
.ad
.RS 10n
The \fIfildes\fR argument is not a valid open file descriptor.
.RE

.sp
.ne 2
.na
\fB\fBEINTR\fR\fR
.ad
.RS 10n
A signal was caught during the execution of the \fBioctl()\fR function.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The stream or multiplexer referenced by \fIfildes\fR is linked (directly or
indirectly) downstream from a multiplexer.
.RE

.sp
.LP
The \fBioctl()\fR function will also fail if the device driver detects an
error.  In this case, the error is passed through \fBioctl()\fR without change
to the caller. A particular driver might not have all of the following error
cases. Under the following conditions, requests to device drivers may fail and
set \fBerrno\fR to indicate the error
.sp
.ne 2
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 11n
The \fIrequest\fR argument requires a data transfer to or from a buffer pointed
to by \fIarg\fR, but \fIarg\fR points to an illegal address.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 11n
The \fIrequest\fR or \fIarg\fR argument is not valid for this device.
Many devices return \fBENOTTY\fR for an unknown \fIrequest\fR.
.RE

.sp
.ne 2
.na
\fB\fBEIO\fR\fR
.ad
.RS 11n
Some physical I/O error has occurred.
.RE

.sp
.ne 2
.na
\fB\fBENOLINK\fR\fR
.ad
.RS 11n
The \fIfildes\fR argument is on a remote machine and the link to that machine
is no longer active.
.RE

.sp
.ne 2
.na
\fB\fBENOTTY\fR\fR
.ad
.RS 11n
The \fIfildes\fR argument is not associated with a device that accepts
control functions.
.sp
The device driver does not know the \fIrequest\fR command.
.RE

.sp
.ne 2
.na
\fB\fBENXIO\fR\fR
.ad
.RS 11n
The \fIrequest\fR and \fIarg\fR arguments are valid for this device driver, but
the service requested can not be performed on this particular subdevice.
.sp
The device driver does not support the \fBioctl()\fR function.
.RE

.sp
.ne 2
.na
\fB\fBENODEV\fR\fR
.ad
.RS 11n
The \fIfildes\fR argument refers to a valid streams device, but the
corresponding device driver does not support the \fBioctl()\fR function.
.RE

.sp
.LP
Streams errors are described in \fBstreamio\fR(4I).
.SH ATTRIBUTES
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
.TE

.SH SEE ALSO
.BR streamio (4I),
.BR termio (4I),
.BR attributes (7),
.BR standards (7)
